Introduction:
Cattley guava (Psidium cattleianum)
Psidium cattleianum is native to Brazil, but has been naturalised in Florida, Hawai’i, tropical Polynesia, Norfolk Island and Mauritius for its edible fruit. It forms thickets and shades out native vegetation in tropical forests and woodlands. It has had a devastating effect on native habitats in Mauritius and is considered the worst plant pest in Hawai’i, where it has invaded a variety of natural areas. It benefits from feral pigs (Sus scrofa) which, by feeding on its fruit, serve as a dispersal agent for its seeds. In turn, the guava provides favourable conditions for feral pigs, facilitating further habitat degradation.
Description:
Evergreen shrub or small tree up to 8m tall. Mature branches are gray to reddish-brown with peeling bark and young branches are round and pubescent. Leaves are opposite, simple, entire, glabrous, elliptic to oblong, to 8cm (3 in) long. Flowers to 2.5cm (1.2 in) wide, born singly at leaf axils, with white petals and numerous white and yellow stamens. Fruit is a globose berry, 3-6cm (1.2-2.4 in) long, purple-red, with whitish flesh, usually sweet-tasting when ripe; seeds are numerous.
Occurs in:
Agricultural areas, coastland, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands.
Cattley guava (Psidium cattleianum) Distribution in North America shown in Green.
Habitat description:
Psidium cattleianum is found on various Polynesian and Micronesian islands where it occurs as an introduced species on both disturbed land and in native ecosystems. Habitats it is found in include: sub-montane rainforest, montane cloud forest, montane rainforest, moist tropical montane forest, tropical ravine/riperian forest, tropical evergreen forest, deciduous woodland (oak), tropical montane savanna, lowland sub-tropical rainforest, scrub land, grass land, degraded forest, cultivation and agro-forestry.
General impacts:
P. cattleianum is a habitat-altering weed that poses a major threat to endemic flora by competing for light and soil nutrients. Today the most serious threat to Seychelles forests is the low regeneration of native trees caused by the invasion of alien plant species such as P. cattleianum.
Management information:
Preventative measures:A Risk Assessment of Psidium cattleianum for Hawai‘i and other Pacific islands was prepared.The alien plant screening system is for use in Pacific islands. The result is a score of 18 and a recommendation of: “Likely to cause significant ecological or
Close up of Cattley guava (Psidium cattleianum).
economic harm in Hawai‘i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology and behaviour in Hawai‘i and/or other parts of the world.”
Physical: Because of the huge quantities of seed that are dispersed by feral pigs, and other exotic invasive species, feral species management is a practical and necessary first step in strawberry guava management. Manual and mechanical control measures work reasonably well and are recommended where practical. Seedlings and saplings originating from seed can be uprooted. Uprooted plants may resprout or re-root in areas with greater than 2000mm of rain/year or drier areas after prolonged rain, especially if the plants are set on the ground. Manual and mechanical methods are less effective on root sprouts.Biological: Biological control is the only feasible long-term management strategy for strawberry guava. However, until recently, biological control has been perceived as unfeasible because common guava, grown commercially in Hawai‘i, is a congener of strawberry guava. Biological control is being reexamined. Several insects defoliate strawberry guava in its natural range, it is possible that insect biological control agents could be found that do not attack common guava. Memoranda of agreement has been concluded between the University of Hawai‘i and two Brazilian Universities to locate species attacking strawberry guava and not common guava. It is thought that highly specific insect pests can be found because common guava and strawberry guava are sympatric in their natural range.
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